﻿#define _CRT_SECURE_NO_WARNINGS 1


//542. 01 矩阵
class Solution {
    int dx[4] = { 0, 0, 1, -1 };
    int dy[4] = { 1, -1, 0, 0 };
public:
    vector<vector<int>> updateMatrix(vector<vector<int>>& mat) {

        int m = mat.size(), n = mat[0].size();

        // dist[i][j] == -1 表⽰：没有搜索过
        // dist[i][j] != -1 表⽰：最短距离
        vector<vector<int>> dist(m, vector<int>(n, -1));
        queue<pair<int, int>> q;

        // 1. 把所有的源点加⼊到队列中
        for (int i = 0; i < m; ++i)
            for (int j = 0; j < n; ++j)
                if (mat[i][j] == 0)
                {
                    q.push({ i,j });
                    dist[i][j] = 0;
                }

        // 2. ⼀层⼀层的往外扩 (因为dist每个起点的开始层数了,因此不用再搞一个sz)
        while (q.size())
        {
            auto [a, b] = q.front();
            q.pop();
            for (int k = 0; k < 4; ++k)
            {
                int x = a + dx[k], y = b + dy[k];
                if (x >= 0 && x < m && y >= 0 && y < n && dict[x][y] == -1)
                {
                    dict[x][y] = dict[a][b] + 1;
                    q.push({ x,y });
                }
            }

        }
        return dist;

    }
};